The United States and Japan will step up their defence cooperation to deal with the threat from nuclear-armed North Korea as tensions in East Asia remain high, officials from the two allies said on Thursday.

Antarctic ice-drill a climate snapshot

Antarctic science's holy grail of a million-year climate record is a step closer following a successful ice-drilling expedition.

Australian Antarctic Division (AAD) scientists have returned to Hobart with two tonnes of ice-cores dating back 2000 years and say a record of the climate over a million years could be achievable within a decade.

The Australians were part of an international team that drilled down 300 metres at a site 500km inland from Casey station.

The AAD's chief scientist Dr Nick Gales says, as well as providing a snapshot of the climate over the past 2000 years, the drill is a step towards the goal of a million.

"We have to find exactly the right area where there's very deep ice and it's moving very slowly," Dr Gales told reporters at the AAD's headquarters near Hobart.

"This core gives us more information about where that site might be."

Dr Gales said China had already begun some deeper drilling and an international effort could be underway in five to 10 years.